Small-scale of spectrophotometric determination of polyoxyethylene non-ionic surfactants with ferric thiocyanate complexation following toluene extraction

The spectrophtometric determination of polyoxyethylene non-ionic surfactants (NS) utilizing ferric thiocyanate complex formation preceded by direct toluene-extraction was miniaturized. The consumption of the reagents used was drastically decreased to ca.1/5. Linear relationships between the concentration and the absorbance at 510 nm for the standard heptaoxyethylenedodecylether ranged from 0.1 to 2.0 mg/l. The sensitivity of the method was ca. 24-times higher than that obtained in the cobalt(II)-thiocyanate method (Japanese Industrial Standard). Although the developed method is practically acceptable for environmental analyses, the coexistence of cationic surfactants tended to cause significantly positive errors for NS determinations, which indicated that cationic surfactants should be removed before toluene extraction. The method was applied to the determination of NS in synthetic detergents.